The present invention generally relates to biological shield assemblies of the type surrounding nuclear reactor pressure vessels. In particular, the present invention is directed to a unique, thermally-insulated biological shield assembly which eliminates the need for attaching thermal insulation to the reactor vessel itself.
In order to safely protect the immediate environment about a nuclear reactor pressure vessel, it has become standard practice to position the pressure vessel within a biological shield assembly which usually takes the form of a hollow, concrete body. In addition, a layer of thermal insulation must be positioned between the pressure vessel and concrete body to absorb the relatively high level of heat transmitted outwardly from the pressure vessel during operation of the nuclear reactor.
One of the problems facing known biological shield assemblies is the inability to easily position the thermal insulation between the concrete body and the pressure vessel enclosed therein. Known assemblies suggest attaching the thermal insulation directly to the outer wall of the pressure vessel. This approach has proven generally less than completely satisfactory, in that such a structure severely reduces direct access to the pressure vessel as may be required for maintenance and the like. Because the insulation must be formed with a high degree of accuracy to properly fit the pressure vessel, the overall manufacturing and installation costs are relatively great.
Another approach employed by prior art assemblies is to attach the thermal insulation directly to the concrete body itself. This approach has also proven less than completely satisfactory, in that a relatively large amount of time is required to attach the thermal insulation directly to the concrete shield. Furthermore, such structures generally fail to provide efficient and adequate passageways for the removal of heat from the immediate vicinity of the concrete. As a result, the concentration of heat causes a build-up of thermal stress in the concrete, which reduces the ability of the concrete body to endure pressure shocks, as may occur when a reactor tube within the pressure vessel accidently ruptures.
As will be discussed in detail hereinafter, the present invention provides a thermally-insulated biological shield assembly capable of overcoming each of the aforestated problems, while at the same time effectively preventing the build-up of heat in the immediate vicinity of the concrete body through a combination of thermal insulation and flow passageways.